COS will be abandoned as you left US while it was pending. Same goes for your wife if she left US while H-1 was pending.

You can either apply for COS after you return to US and your H-1 has been approved; or you can enter US on stamped H-1 visa

COS would not be approved as you left US while it was pending

Like explained above, COS would be abandoned. Whenever your new COS gets approved, your wife will have to move to her own H-1 or become dependent on H-4. She will have to maintain that status.

No grace period.

What you can do is file your L-1 to H-1 COS after you return from India and your H-1 has been approved. In COS application mention start date of Oct 1. This way you would remain on L-1 until Oct 1 even if COS gets approved earlier and your wife can continue to work on L-2. Come Oct 1, you will be on H-1 and your wife will be on her H-1 (see (1) for exception).